Computer-implemented method for determining centring parameters for mobile terminals, mobile terminal and computer program

ABSTRACT

Methods and devices for determining at least one centring parameter are disclosed. A mobile terminal is moved from a first position to a second position, and a respective image is captured of an eye area of a person. The acceleration is also measured during the movement. The centring parameter is then determined based on the captured image and the measured acceleration.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of international patentapplication PCT/EP2021/062313, filed May 10, 2021, designating the U.S.and claiming priority to European patent application EP 20 176 093.1,filed May 22, 2020, both of which are hereby incorporated by referencein their entireties.

TECHNICAL FIELD

The present application relates to computer-implemented methods fordetermining centration parameters for a mobile terminal, correspondingmobile terminals and computer programs.

BACKGROUND

A mobile terminal should be understood to mean a device which comprisesat least one programmable processor, a display, and also a camera and anacceleration sensor, and which is designed to be carried, i.e., isconfigured in respect of dimensions and weight so that a person iscapable of carrying it along. Typical examples of such mobile terminalsare smartphones or tablet PCs, which nowadays in almost all availablemodels have a sensor screen (usually referred to as touchscreen), one ormore cameras, acceleration sensors and other sensors such as gyroscopesensors and further components such as wireless interfaces for mobileradio or WLAN (Wireless LAN). The weight of such mobile terminals istypically less than 2 kg, usually less than 1 kg, and far less than thatstill. Computer programs for such mobile terminals are usually referredto as apps (short for the English word “application,” i.e., applicationprogram).

In order to arrange, i.e., to center, spectacle lenses correctly in aspectacle frame, such that the spectacle lenses are worn in a correctposition relative to the eyes of a person who is intended to wearspectacles, so-called centration parameters are used. Some of thesecentration parameters are defined for example in section 5 of thestandard DIN EN ISO 13666: 2012 and comprise for example the pupillarydistance PD in accordance with point 5.29 of this standard. Another ofthese centration parameters is the box height of the boxing systemmentioned in 5.1 of this standard and defined in more specific detail inthe standard DIN EN ISO 8624:2015.

Apparatuses and methods which enable such centration parameters to bedetermined automatically have been developed in recent years. In thisregard, the Zeiss Visufit 1000 is a centration system which uses aninherently calibrated camera system in order to capture at least one eyearea of a person's head, with a spectacle frame being worn, from aplurality of directions and to determine the centration parameterstherefrom. This device is stationary and intended for application on thepart of an optician.

Other procedures use a measuring brace which is attached to thespectacle frame and serves as a reference. Such procedures are knownfrom U.S. Pat. No. 9,928,421 B1, U.S. Pat. No. 9,971,172 B1, U.S. Pat.No. 7,950,800 B1, U.S. Pat. No. 8,360,580 B1, or U.S. Pat. No. 9,535,270B2.

In U.S. Pat. No. 9,928,421 B1, a person wearing spectacles and ameasuring brace is recorded from different directions in that case.During the recordings, an inclination angle of the camera used for therespective recordings is ascertained such that an inclined arrangementof the camera can be taken into account. Centration parameters are thendetermined from the recordings.

U.S. Pat. No. 9,971,172 B1 discloses a centration device in whichdimensions of a spectacle frame that are projected onto an image planecan be corrected in relation to a head posture in order to be able todetermine centration data as accurately as possible even in the case ofrelatively large inclination angles of a camera used and rotation anglesof the head. In that case, a single front image of the head is used,that is to say an image recording from the front, required inclinationand rotation angles being determined from the imaging of a measuringbrace.

U.S. Pat. No. 7,950,800 B1 discloses determining centration data, whichonce again involves using a measuring brace in order to offer a scalefor recordings by a camera which records a front view of a person. Aninclination of the camera is once again taken into account in that case.

U.S. Pat. No. 8,360,580 B1 describes how the so-called center ofrotation of the eye can be determined with the aid of image capture by acamera and the use of marking elements on the head of a person. Theposition of the center of rotation of the eye is relevant in thecalculation of centration parameters if the viewing direction adopted atthe time of capture does not correspond to the so-called distance-visionviewing direction, where the person's gaze is directed essentially toinfinity. In this document, the position of the center of rotation ofthe eye is determined with the aid of two captured recordings that imagethe person with different viewing directions. Markings on the head areused in order to be able to determine absolute sizes.

U.S. Pat. No. 7,950,800 B1 also describes methods for determiningcentration parameters by means of a handheld camera, with a measuringbrace once again being used as an absolute size scale.

U.S. Pat. No. 9,535,270 B2 discloses a method in which a stationaryvideo camera records a person while the person raises his/her head andpays attention to a stationary target in the process. In that case, asignal of an inclinometer selects, from the resultant series of imagerecordings during the raising of the head, that recording which bestreproduces a normal head posture. In that case, the face is recorded bya front camera of a tablet PC. A measuring brace worn by the person isimaged by both cameras, that is to say the video camera and the frontcamera of the tablet PC. In that case, the two cameras form an angle ofapproximately 30°. Centration parameters are then determined from theimage recordings.

The methods and apparatuses described above necessarily require ameasuring brace (or other scale) or a multi-camera system and areintended, in principle, for implementation by an optician or anotherappropriately trained person. Both methods are suitable primarily forthe field of stationary use, and only to a limited extent for mobileterminals.

U.S. 2018/140 186 A1 describes a method according to the preamble ofclaim 1. DE 10 2011 009 646 A1 describes a further method which uses aplurality of image recordings and the measurement of an acceleration.

SUMMARY

There is a need for simplified procedures for determining at least somecentration parameters which can be implemented by means of a mobileterminal such as a smartphone or tablet PC and which can be implementedin particular by a person who is actually to be examined, withoutrelatively high complexity. Proceeding from methods and apparatuseswhich use measuring braces, for example as in U.S. Pat. No. 7,950,800B1, it is an aspect of the disclosure to provide methods and apparatusesin which such measuring braces or other aids are at least not absolutelynecessary.

This object is achieved in accordance with a first aspect of thedisclosure by means of a computer-implemented method and a correspondingmobile terminal taking into account image angle properties of thecamera, the image angle properties specifying pixels of an image sensorof the camera, is achieved in accordance with a second aspect of thedisclosure by means of a computer-implemented method and a correspondingmobile terminal, taking into account a rectilinear movement of themobile terminal parallel to the optical axis of the camera toward theeye area or away from the eye area, is achieved in accordance with athird aspect of the disclosure by means of a computer-intimated methodand a corresponding mobile terminal, taking into account a 3D model ofthe eye area, and is achieved in accordance with a fourth aspect of thedisclosure by means of a computer-implemented method and a correspondingmobile terminal, taking into account that corneal vertex distance isdetermined as a difference between the distance between the camera andthe pupil and the distance between the camera and the spectacle frame.Further exemplary embodiments and also a method for fitting spectaclelenses by grinding are disclosed below. Corresponding computer programsare additionally provided.

According to the disclosure, in all aspects, a computer-implementedmethod for a mobile terminal is provided, comprising:

-   -   capturing a first image of at least one eye area of a person by        means of a camera of the mobile terminal at a first position of        the mobile terminal,    -   capturing a second image of the eye area of the person by means        of the camera at a second position of the mobile terminal, and        determining at least one centration parameter on the basis of        the first image and the second image.

The method comprises repeated measurement of an acceleration of themobile terminal during a movement of the mobile terminal from the firstposition to the second position. The at least one centration parameteris then additionally ascertained on the basis of the repeatedly measuredacceleration.

The second image need not necessarily be captured after the first image.By way of example, a video sequence comprising a multiplicity of images,including the first image and the second image, can be captured, whereinone further image or a plurality of further images of the multiplicityof images can lie between the first image and the second image.Additionally or alternatively, one further image or a plurality offurther images of the multiplicity of images can also precede the firstimage or succeed the second image. The method can also additionally usesuch further images and associated positions and accelerations fordetermining centration parameters.

The at least one centration parameter can comprise the pupillarydistance. If the person is wearing a spectacle frame, the at least onecentration parameter can additionally or alternatively comprise a heightof the boxing system of the spectacle frame or other measures of theboxing system of the spectacle frame. In this regard, the pupillarydistance or measures of the boxing system can be determined in a simplemanner.

The eye area of a person is a part of the person's face which includesat least the person's eyes and, if the person is wearing a spectacleframe, a spectacle frame worn by the person. Here, pursuant to DIN ESO7998:2006-01 and DIN ESO 8624:2015-12, a spectacle frame should beunderstood to mean a frame or a holder by means of which spectaclelenses can be worn on the head. In particular, the term as used hereinalso includes rimless spectacle frames. Colloquially, spectacle framesare also referred to as frames.

Such a method does not require an additional scale such as a measuringbrace or measurement points on a head of the person. By means ofrepeated measurement of the acceleration, it is possible, by integratingthe acceleration twice, to determine a path of the mobile terminal fromthe first position to the second position, in particular a distancebetween the first position and the second position. This then makes itpossible to determine the at least one centration parameter withoutusing a scale. In this case, repeated measurement is understood to meanmeasurement with a rate, i.e., a number of measurement values per unittime, such that the path of the mobile terminal can be determinedsufficiently accurately in order to be able to determine the centrationparameters accurately enough for the spectacle lens centration. In thecase of customary mobile terminals, the acceleration measured by abuilt-in acceleration sensor of the mobile terminal is digitallyprocessed with a sampling rate. A sampling rate of 10 Hz, i.e., 10acquired measurement values per second, or even less than that, may besufficient for the method according to the disclosure. In this case, themeasurement values can be subjected to low-pass filtering in order toincrease the accuracy. Higher sampling rates are likewise possible andcan increase the accuracy. The sampling rate is upwardly limited by thespeed of the hardware components of the mobile terminal. In this case, acontinuous measurement can be approximated by high sampling rates.

A camera and a sensor for measuring the acceleration are presentpractically in every commercially available mobile terminal such as asmartphone or a tablet PC. Consequently, by means of simply providing acomputer program for the mobile terminal, that is to say an app, it ispossible for the above method to be implemented without additionalhardware being required.

For the purpose of acquiring the at least one centration parameter, theposition of the pupils in the first image and the second image and/orthe spectacle frame in the first image and second image can beidentified by means of conventional image processing methods. For theframe rim of a spectacle frame, such methods are described in EP 3 355214 A1, for example. For the purpose of detecting the position of thepupils in the image, corresponding methods are described in S. Kim etal., “A Fast Center of Pupil Detection Algorithm for VOG-Based EyeMovement Tracking,” Conf Proc IEEE Eng Med Biol Soc. 2005; 3:3188-91 orin Mansour Asadifard and Jamshid Shanbezadeh, “Automatic Adaptive Centerof Pupil Detection Using Face Detection and CDF Analysis,” Proceedingsof the International MultiConference of Engineers and ComputerScientists 2010 Vol I, IMECS 2010, Mar. 17-19, 2010, Hong Kong.

In this aspect, preferably also in the other aspects, determining the atleast one centration parameter is additionally effected on the basis ofimage angle properties of the camera. These image angle propertiesspecify the pixels of an image sensor of the camera on which an objectwhich is at a specific angle with respect to the optical axis of thecamera is imaged. In other words, the image angle properties specify acorrelation between this angle with respect to the optical axis and thepixel. In this case, the optical axis denotes at the camera an axis ofsymmetry of the optical system of the camera, which system is usuallyrotationally symmetrical.

Such image angle properties thus enable an assignment between pixels inwhich objects such as, for example, the pupils are captured and angles,which enables corresponding centration parameters to be calculated in asimple manner.

The image angle properties of the camera can be determined for examplefrom manufacturer specifications regarding the image angle of a lens ofthe camera. However, in the first aspect, optionally also in otheraspects, in the context of the computer-implemented method, the imageangle properties are determined beforehand by a first determinationimage and a second determination image being captured by means of thecamera, the mobile terminal being rotated between capturing the firstdetermination image and the second determination image. In the first andsecond determination images, mutually corresponding objects (that is tosay objects which are visible in both images) are then identified bymeans of image processing. The image angle properties can then bedetermined from the rotation, which can be measured by an orientation oracceleration sensor of the mobile terminal, and from the pixels on whichthe objects in the first and second determination images are imaged. Byvirtue of such a determination of the image angle properties, as in thefirst aspect, no specifications on the part of the manufacturer areneeded.

For the purpose of carrying out the method, the mobile terminal canissue corresponding instructions to a person who is carrying out themethod. This can be done for example via a loudspeaker of the mobileterminal or a display of the mobile terminal. By way of example, theperson who is carrying out the method can be instructed to move themobile terminal from the first position into the second position. Itshould be noted that the person who is carrying out the method can beidentical with the person whose centration data are being determined,with the result that no optician is required. By virtue of the issuingof the instructions, even an untrained person can carry out the method.

The method can furthermore comprise measuring an orientation of themobile terminal at the first position, at the second position and/orduring the movement from the first position into the second position.Here the orientation indicates how the mobile terminal is oriented atthe position at which it is situated in each case, and indicates aninclination of the mobile terminal, for example. The orientation can bespecified for example by means of three angles with respect to the axisof a fixed coordination system. The orientation of the mobile terminalthen corresponds to the orientation of the camera of the mobileterminal. The combination of orientation and position is referred tosometimes, in particular in robotics, as pose, cf. DIN EN ISO 8373:2012.

In some exemplary embodiments, the determination of the at least onecentration parameter can then additionally be performed on the basis ofthe orientation e.g., at the first position and/or second position.Effects resulting from the orientation can be compensated for as aresult. By way of example, distances in the captured image may appeardifferent depending on orientation, and such effects can be compensatedfor. This is based essentially on simple geometric considerations of howthe eye area is imaged onto the image sensor of the camera depending onthe orientation.

In an alternative exemplary embodiment, a message can be issued if theorientation of the mobile terminal deviates from a predefinedorientation. This message can be a warning, combined with instructionsto move the mobile terminal to the predefined orientation again. In thiscase, the predefined orientation is an orientation on which thedetermination of the at least one centration parameter is based, that isto say formulae and the like for the calculation of the at least onecentration parameter proceed from this predefined orientation. Thepredefined orientation can be for example a vertical orientation of adisplay of the mobile terminal. In this case, different orientations donot have to be taken into account computationally, which simplifies thecalculation, rather the person who is carrying out the method is urgedto maintain the mobile terminal in the predefined orientation.

The movement can be a rectilinear movement toward or away from the eyearea, such that the first position and the second position are capturedat two different distances from the eye area. This is the case in thefourth aspect, optionally also in other aspects. The person who iscarrying out the method can once again be given correspondinginstructions for this purpose. This enables a relatively simplecalculation, which is explained in greater detail later with referenceto corresponding figures.

The movement can also be a movement substantially in a plane in front ofthe eye area, for example an arcuate movement. Here the centrationparameters are then ascertained from the first image and the secondimage in the third aspect, optionally also in the first and secondaspects, in a manner similar to triangulation (cf. The article“Triangulation (Messtechnik)” [“Triangulation (metrology)”] in theGerman-language Wikipedia, version on Apr. 13, 2018).

It should be noted that, over and above the use of the acceleration, amore extensive ascertainment of position and orientation of the mobileterminal, i.e., of the pose of the mobile terminal, is also possible,for example as described in S.-H. Jung and C. Taylor, “Camera trajectoryestimation using inertial sensor measurements and structure from motionresults,” in Proceedings of the IEEE Computer Society, Conference onComputer Vision and Pattern Recognition, vol. 2, 2001, pp.11-732-11-737″ and Gabriel Mitzi, Stephan Weiss, Davide Scaramuzza,Roland Stiegwart, “Fusion of IMO and Vision for Absolute ScaleEstimation in Monocular SLAM, available at the urldoi.org/10.1007/s10846-010-9490-z”. Sensor fusion techniques such as in“Sensor Fusion on Android Devices: A Revolution in Motion Processing(InvenSense, available at the urlwww.youtube.com/watch?v=C7JQ7Rpwn2k&feature=youtu.be)” can also be used.

In this case, a plurality of images comprising more than just the firstimage and the second image can also be captured during the movement.From such a plurality of images, in the second aspect, optionally alsoin the other aspects, a 3D model of the eye area or of the head is thencreated, in a similar manner to what is done in the device Visufit 1000from Zeiss, cited in the introduction, on the basis of a plurality ofcamera images. From this 3D model of the head, optionally with aspectacle frame, centration parameters can then be ascertained as in thecase of this stationary centration device.

A model, in particular a 3D model, should be understood to mean athree-dimensional representation of real objects, in this case the eyearea, optionally with a spectacle frame, which are available as a dataset in a storage medium, for example a memory of a computer or a datacarrier. By way of example, such a three-dimensional representation canbe a 3D mesh, consisting of a set of 3D points, which are also referredto as vertices, and connections between the points, which connectionsare also referred to as edges. In the simplest case, these connectionsform a triangle mesh. Such a representation as a 3D mesh describes onlythe surface of an object and not the volume. The mesh need notnecessarily be closed.

In this case, the 3D model can be a simplified 3D model which specifiesthe position of the pupils and the position of the spectacle frame, thelatter represented in accordance with the boxing system. In this case,the position of the pupils when looking straight ahead into the distancecan be determined indirectly by way of the position of the mechanicalcenter of rotation of the eye, as will also be explained later withreference to figures. In this case, according to the internet linkwww.spektrum.de/lexikon/optik/augendrehpunkt/264, the mechanical centerof rotation of the eye is that point of the eye which changes itsposition the least during changes in the viewing direction,and—according to this source—lies on average 13.5 mm behind the anteriorcorneal vertex.

Techniques of simultaneous position determination and mapping that areknown from robotics can be used for this purpose; see, for example, theWikipedia article “simultaneous localization and mapping” in theGerman-language Wikipedia, version on Apr. 14, 2018, with the furtherreferences given there.

Moreover, generally by means of repeatedly capturing images withconventional procedures of error computation, it is possible to increasean accuracy by the plurality of images being treated as a plurality ofmeasurements.

In the above exemplary embodiments, a plane of an image sensor of thecamera and a plane of the spectacle frame are kept substantiallyparallel. A measurement of the “as-worn” pantoscopic angle (defined inDIN EN ISO 1366 6: 2012; page 18) is not possible in a practical andtargeted manner. In some exemplary embodiments, the “as-worn”pantoscopic angle can be input, and can influence the determined 3Dmodel. The same applies to the corneal vertex distance in accordancewith DIN EN ISO 1366 6: 2012; page 27, which can likewise be inputseparately. In the fourth aspect, by contrast, the corneal vertexdistance is determined by a first distance between the camera and thespectacle frame and a second distance between the camera and a pupil ofthe person being determined and the corneal vertex distance beingdetermined as the difference between the second distance and the firstdistance. In this regard, the corneal vertex distance can be determinedeven in the case of a rectilinear movement of the camera.

In other exemplary embodiments, the “as-worn” pantoscopic angle can alsobe measured by the mobile terminal being moved for example in ahemisphere or other three-dimensional movements in front of the face ofthe eye area and a 3D model which takes account of the “as-worn”pantoscopic angle thus being able to be created. In this case, athree-dimensional movement is a movement which comprises components inthree linearly independent spatial directions.

Even if the methods described above are implementable without ameasuring brace or other scale, in some exemplary embodiments such ascale can be provided, which is to be fitted at the eye area of theperson. In this case, a scale is a device whose size is known and whichcan therefore serve as a size reference in the first image or secondimage. However, the accuracy of the methods described can also beincreased, particularly when creating a 3D model as described above.

In other exemplary embodiments, a dimension of a spectacle frame worn bythe person can be provided by way of an input on the mobile terminal.Such a dimension can be the height or width of the spectacle frame inthe boxing system. This can be specified by a manufacturer of thespectacle frame or be gauged manually. This likewise provides a scalefor the first image and the second image by the spectacle frame in theseimages being identified as explained above and the dimension in theimage being related to the dimension that is input. This, too, isoptional, however, and other exemplary embodiments require neither aninput of a dimension nor an external scale.

In accordance with a further exemplary embodiment, a mobile terminal isprovided, comprising a processor, a camera and an acceleration sensor.In this case, the processor is programmed, for example by way of acomputer program stored in a memory of the mobile terminal, to carry outone of the methods described above, that is to say to cause a firstimage of an eye area to be captured at a first position of the mobileterminal, a second image of the eye area to be captured at a secondposition of the mobile terminal and centration parameters to bedetermined on the basis of the first image and the second image. Thisinvolves repeated measurement of an acceleration of the mobile terminalduring the movement from the first position into the second position,and the determination of the centration parameter is additionally basedon the basis of the repeated measurement of the acceleration.

Finally, a computer program for a mobile terminal, that is to say anapp, is also provided which, when it is executed on the mobile terminal,has the effect that one of the methods described above is carried out.This computer program can be stored on a nonvolatile data carrier suchas a memory card, a hard disk, an optical data carrier such as a DVD orCD and the like or can be transmitted by way of a data carrier signal.

The centration parameters determined can then be used for fitting aspectacle lens by grinding in a manner known per se. Accordingly, amethod for fitting a spectacle lens by grinding using the at least onecentration parameter which is determined by one of the above methods isalso provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will now be described with reference to the drawingswherein:

FIG. 1 shows a block diagram of a mobile terminal such as is used inexemplary embodiments;

FIG. 2 shows a flow diagram of a method for determining at least onecentration parameter in accordance with one exemplary embodiment;

FIG. 3 shows a diagram for elucidating the determination of image angleproperties of the camera;

FIG. 4 shows a diagram for elucidating one possible implementation ofsteps 21 to 23 from FIG. 2 ;

FIGS. 5A to 5C show diagrams for elucidating the determination of adistance Δz from FIG. 4 on the basis of acceleration data;

FIG. 6 shows a diagram for elucidating the determination of a pupillarydistance in the implementation from FIG. 4 ;

FIG. 7 shows a diagram for elucidating a further possible implementationof steps 21 to 23 of the method from FIG. 2 ; and

FIGS. 8A and 8B show diagrams for elucidating the determination of aposition of the center of rotation of the eye or of the pupil.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The exemplary embodiments described below use a mobile terminal fordetermining the pupillary distance and also a height of the boxingsystem of a spectacle frame and optionally other centration parameters.FIG. 1 shows a block diagram of a mobile terminal 10 such as is used insuch exemplary embodiments. The mobile terminal here can be a smartphoneor a tablet computer. Smartphones or tablet computers available nowadaystypically have at least the components illustrated in FIG. 1 , but canalso have further components.

The mobile terminal 10 in FIG. 1 has a sensor screen 19 (referred to as“touchscreen”), which serves as an input device and also for outputtingfor example instructions to a person. The mobile terminal 10 iscontrolled by a processor 16, which can access a memory 15, in whichcomputer programs can be stored. As already mentioned in theintroduction, such computer programs for mobile terminals are alsoreferred to as apps. In the case of the mobile terminal 10, a computerprogram for carrying out one of the methods described below is stored inthe memory 15.

The mobile terminal 10 furthermore has a loudspeaker 13 for outputtingsounds, and a microphone 14. Via the loudspeaker 13, instructions can beoutput to a person who is carrying out the method, and voice commands,for example, can be received via the microphone 14.

The mobile terminal 10 furthermore has a front camera 11 and a rearcamera 12. In this case, the front camera 11 is arranged on the sameside as the sensor screen 19, such that a person, in particular the eyearea of a person observing the sensor screen 19, can be captured bymeans of the front camera 11. The rear camera 12 is arranged on theopposite side of the mobile terminal 10 to the sensor screen 19.

Furthermore, the mobile terminal 10 has an acceleration sensor 17, bymeans of which accelerations of the mobile terminal 10 can be measured,and also an orientation sensor 110, by means of which an orientation ofthe mobile terminal 10 can be measured. Such an orientation sensor issometimes also referred to as an inclination sensor. It should be notedthat the acceleration sensor 17 and the orientation sensor 110 areillustrated as separate components in FIG. 1 in order to elucidate thedifferent functions used in the context of the methods described below.However, the functions can also be provided by a common sensor device.

Finally, provision is made of a communication circuit 10 fortransmitting (TX, from “transmitter”) and receiving (RX, from“receiver”) data, for example via a mobile radio network and/or via aWLAN network (“Wireless LAN”). Via these communication circuits, thecentration data determined can be transmitted to an optician, forexample, who then uses this data for fitting spectacle lenses bygrinding.

FIG. 2 shows a flow diagram for elucidating a method in accordance withone exemplary embodiment, which is realized by corresponding programmingof the processor 16 of the mobile terminal 10. For elucidating the stepsof the method in FIG. 2 , reference is made to FIGS. 3 to 7 .

In step 20, the image angle properties of a camera used for thesubsequent steps, i.e., of the front camera 11 or of the rear camera 12,of the mobile terminal, can optionally be determined. This determinationneed only be carried out once and is not carried out each time thefollowing steps are carried out. As an alternative to optional step 20,the image angle properties can also be obtained in a different way. Byway of example, the image angle properties can already be present asmanufacturer specifications and then be input, or in some cases they canalso be stored in the mobile terminal by the manufacturer and then beread out from the memory.

One implementation of step 20 will be explained with reference to FIG. 3. In this case, FIG. 3 shows an image sensor 30 of the camera 11 or 12,which sensor has a multiplicity of pixels 31, in a cross-sectional view.For elucidation purposes, ten pixels 31 are illustrated, which from leftto right are designated by A to J (that is to say 31A to 31J). In thiscase, resolutions of typical cameras of mobile terminals are in therange of several megapixels, and so the illustration in FIG. 3 issimplified in order to be able to better elucidate the procedure.

Firstly, an image with a plurality of objects is captured in a firstorientation of the image sensor 30. One object 32 is illustrated here asan example. The captured objects such as the object 32 are preferablysituated at a relatively large distance from the image sensor 30, forexample >1 m, >5 m or >10 m, in order to minimize errors owing to cameramovements. In the simplified example in FIG. 3 , the object 32 is imagedonto the pixel 31I by an optical unit (not illustrated). The opticalaxis of the camera is designated by 33.

The camera is then rotated about an axis perpendicular to the imageplane in FIG. 3 . The image sensor 30 in this new position is designatedby 30′. In this rotated position, the object is now at a different anglewith respect to the optical axis 33 (designated by 33′ for the position30′), and the object 32 is now imaged onto the pixel 31′G. The object 32can be recognized in both captured images by means of the image analysismethods already mentioned. This can be done for a multiplicity of suchobjects 32. From the displacements of the objects between the twoimages, i.e., the changes regarding the pixels onto which the objectsare imaged, the image angle properties of the camera can then bedetermined. In this case, the angle by which the camera is rotated ismeasured by means of the orientation sensor 110. The rotationillustrated can be effected twice in this case, namely—as regards therotation illustrated in FIG. 3 —about an axis perpendicular to the imageplane and about an axis that is perpendicular thereto and is likewiseparallel to a surface of the image sensor 30. The image angle propertiescan thus be ascertained in two mutually perpendicular directions andthus for an entire—usually— rectangular image sensor in step 20. In thiscase, the determination of the image angle properties can be adverselyaffected by distortions such as pincushion or barrel distortion duringimage capture. However, mobile terminals here usually have an intrinsiccalibration which at least substantially eliminates such distortionscomputationally.

In order to prevent unwanted translations of the camera and thus of theimage sensor 30 during the rotation of the camera from corrupting theresult, a translation of the camera that is possibly superposed on therotation of the camera can be detected and computationally separatedfrom the rotation in order thus to compensate for an influence of thetranslation. Measurement values of the acceleration sensor 17 of themobile terminal and/or the captured images can be used for this purpose.This compensation is facilitated if the captured objects such as theobject 32 are situated at different distances from the camera in theimage field thereof. In this case, the calculation of the translationaccording to a position change can be effected as in the references Junget al. or Mitzi et al., cited above.

In step 21 in FIG. 2 , a first image of an eye area is captured in afirst position of the mobile terminal. In step 22, the mobile terminalis then moved into a second position, the acceleration during themovement from the first position to the second position being measured.In step 23, a second image of the eye area is then captured in a secondposition of the mobile terminal.

One possible implementation of these steps 21-23 is elucidated in FIG. 4. In the case of the implementation in FIG. 4 , firstly an image of aneye area of a person 41, of whom a head is illustrated, is captured in afirst position of the mobile terminal 10, designated by 10A in FIG. 4 .The reference sign 43 designates the right eye of the person, who inthis case is wearing a spectacle frame 42. If the person 41 is carryingout the method, the image capture is expediently effected by means ofthe front camera 11 of the mobile terminal in order that the person canobserve the sensor screen 19 and instructions and indications giventhereon at the same time as the movement. If the method is carried outby some other person, for example an optician, the image capture isexpediently effected by means of the rear camera 12, such that the otherperson can then observe the sensor screen 19. In the case of theimplementation in FIG. 4 , here the mobile terminal is held such thatthe optical axis 33 is directed at the head 41, in particularapproximately at the eye area. This alignment can be checked by means ofthe orientation sensor 110, and for example in the case of anorientation of the mobile terminal 10 from the position illustrated inFIG. 4 , an indication to correctly align the mobile terminal 10 againcan be issued to the person who is carrying out the method.

The mobile terminal 10, as indicated by an arrow 40, is then movedparallel to the direction of the optical axis 33 toward the head 41 intoa second position designated by 10B, and the second image is capturedhere. The correct direction of the movement can once again be checked bymeans of the sensors of the mobile terminal 10 and, if appropriate, anindication can be issued to the person who is carrying out the method.During the movement, the acceleration of the mobile terminal 10 ismeasured by means of the acceleration sensor 17. A distance between thefirst position and the second position is designated by Δz in FIG. 4 .In this case, the camera is kept approximately at the level of thepupils, and the eyes 43 look at the camera. In this way, the opticalaxis of the camera matches the person's viewing direction.

In the case of the implementation in FIG. 4 , image capture can also beeffected repeatedly during the movement in order to increase theaccuracy.

In step 24, centration parameters are then determined from the firstimage, the second image and the measured acceleration using the imageangle properties of the camera. For the implementation in FIG. 4 , thiswill now be explained with reference to FIGS. 5A to 5C and also 6.

In order to determine centration parameters, firstly the distance Δzbetween the first position and the second position is ascertained on thebasis of the measured acceleration. For the implementation in FIG. 4 ,this will be explained with reference to FIGS. 5A to 5C.

FIG. 5A shows one example of the acceleration a(t) over time t for themovement from the first position 10A to the second position 10B in FIG.4 . In this case, the duration of the movement is from a time t1 to atime t2. The acceleration is firstly positive when the mobile terminal10 is accelerated from the first position 10A, and then negative whenthe mobile terminal 10 is decelerated again in order to come to rest atthe second position 10B. The region in which the acceleration ispositive is designated by F1, and the region in which the accelerationis negative is designated by F2.

Integration of the acceleration yields the velocity, as is shown in FIG.5B. The mobile terminal is at rest at the beginning of the movement (v1)and at the end of the movement (v2), such that the integration constantfor determining the velocity can be set to zero. The area F3, that is tosay the integral of the velocity over time, then yields the desireddistance Δz, as is illustrated in FIG. 5C. The z-position in theposition 10A, designated by z1 in FIG. 5C, can be assumed to be 0 inthis case, since only the value Δz is of interest for the subsequentdetermination and the absolute position is not required.

The calculation of centration parameters will be explained on the basisof the example of the pupillary distance with reference to FIG. 6 . Inthis case, the pupillary distance such as appears at the first position10A in the first image is designated by 60, and the pupillary distancein the second image such as appears at the second position 10B isdesignated by 61. The respective position of the mobile terminal isdesignated by 62. In FIG. 6 , therefore, in order to elucidate thegeometric relationships, the position of the mobile terminal is fixedlydesignated by 62, and the different distances with respect to the head41 are illustrated by different distances of the pupillary distance 60and 61, respectively, from this point 62.

The distance between the mobile terminal at the first position 10A andthe head 41 is designated by D2, and the distance at the second position10B with respect to the head 41 is designated by D1. On the basis of theimage angle properties discussed above, from the positions of the pupilsin the first image and the second image, that is to say from the pixelson which the pupils appear in the first image and in the second image,it is possible to determine an angle α2 for the first image and an angleα1 for the second image at which the pupillary distance appears asviewed from the camera, as is identified in FIG. 6 .

From the values α1, α2 and Δz determined above, it is possible tocalculate the pupillary distance PD as follows:

${\tan\left( {\alpha 2/2} \right)} = {\frac{PD/2}{d2} = \frac{PD/2}{{d1} + {\Delta z}}}$${\tan\left( {\alpha 1/2} \right)} = \frac{PD/2}{d1}$${\frac{1}{\tan\left( {{\alpha 2}/2} \right)} - \frac{{d1} + {\Delta z}}{\frac{PD}{2}}} = {\frac{1}{\tan\left( {\alpha 1/2} \right)} - \frac{d1}{PD/2}}$${\left( {\frac{1}{\tan\left( {{\alpha 2}/2} \right)} - \frac{1}{\tan\left( {{\alpha 1}/2} \right)}} \right)^{- 1}*\Delta z*2} = {PD}$

Other geometric variables from the first image and the second image,such as the height of the spectacle frame in the boxing system or thewidth, can be calculated in the same way. In this case, in the equationsabove, PD is then replaced by the corresponding geometric variable. Inthis way, centration parameters can be determined as dimensions in thefirst and second images in a simple manner.

Additionally, after the calculation of PD, from the equations above, thevalues d1, d2 can also be calculated. Consequently, the distance betweenthe camera of the mobile terminal and the pupils is then known. The samecan be carried out for the spectacle frame. From the difference betweenthe camera-pupil distance and the camera-spectacle frame distance, thecorneal vertex distance as a further centration parameter canadditionally be calculated as the difference between the two distances.

Alternatively, a fixed value for the corneal vertex distance can also beassumed, or the latter can be input from other sources.

FIG. 7 shows an alternative implementation for steps 21 to 23 from FIG.2 . Here the mobile terminal is moved in a plane in front of the eyearea of the head 41, and images of the eye area are captured in at leasttwo positions. Three positions 10A, 10B, 10C along a circular path 70are shown as an example in FIG. 7 . The relative pose of the positionscan be determined by measuring the three-dimensional acceleration duringthe movement between the positions. In this case, a circular path as inFIG. 7 need not be present, rather it is also possible to use some otherpath, for example some other arcuate path.

The centration data, such as the pupillary distance, can then bedetermined in step 24 essentially as in the case of a triangulation, ashas already been explained in the introduction. The orientation of themobile terminal, that is to say the orientation in each of the positionsin which an image is captured, can also be used for this purpose.

The captured recordings in FIG. 7 can be used to create a simplified 3Dmodel comprising the spectacle frame, represented by the measures in theboxing system, and the eyes (represented by the pupils, or by thecenters of rotation of the eyes). In this case, the person lookscontinuously in a defined direction, e.g., directly into the camera orat a known, fixed point in the distance. The positions of the centers ofrotation of the eyes or the positions of the pupils can be determined inthis way. If this is the case, the positions of the centers of rotationof the eyes and therefrom the positions of the pupils and hence thepupillary distance or directly the positions of the pupils of both eyescan thus be determined. These two possibilities will now be explainedwith reference to FIGS. 8A and 8B.

FIG. 8A shows a case in which the person is looking at the mobileterminal 10, which is illustrated in two positions 10A, 10B. The pupilsof the eyes 43A, 43B are illustrated as black dots and in this casefollow the position of the mobile terminal 10, that is to say that theyare directed at the mobile terminal 10 in the respective position 10A or10B. If a triangulation as mentioned above is then carried out on thebasis of the pose of the pupils in the images respectively captured inthe positions 10A, 10B, the result produced is the positions of thecenters of rotation of the eyes, as evident from FIG. 8A, according tothe intersection points of the connecting lines from the positions 10A,10B to the respective positions of the pupils. From these, the positionof the pupils when looking straight ahead into the distance can then beestimated by adding a value of approximately 13.5 mm as average distanceof the center of rotation of the eye from the anterior corneal vertexfrom the position of the centers of rotation of the eyes in the frontaldirection of the person. The pupillary distance can in turn bedetermined from the positions of the pupils estimated in this way.

FIG. 8B illustrates the case in which the person is looking straightahead at a target in the distance, while the mobile terminal capturesimages in the positions 10A, 10B. In this case, the pupils do not followthe mobile terminal 10, and the position of the pupils is determineddirectly by triangulation.

Further details concerning such position calculations on the basis ofcaptured image recordings can also be gathered from U.S. 2013/083976 A,U.S. 2013/076884 A or WO 2015/101737 A1.

The image capture can also be effected repeatedly both in the case ofFIG. 3 and in the case of FIG. 7 , and in accordance with a plurality ofimages it is then possible to increase the accuracy of the determinationof the centration parameters in accordance with a conventional errorcomputation. In the case of the procedure in FIG. 7 , a 3D model can becreated, in particular.

As already mentioned in the introduction, the methods do not require ameasuring brace or other scale. Optionally, such a scale, designated bythe reference sign 71 in FIG. 7 , can additionally be provided as a sizescale in order to increase the accuracy of the determination. Inparticular, this can support the creation of the 3D model in the case ofFIG. 7 .

Some exemplary embodiments are defined by the following clauses:

Clause 1. A computer-implemented method for a mobile terminal fordetermining at least one centration parameter, comprising:

capturing a first image of an eye area of a person at a first positionof the mobile terminal by means of a camera of the mobile terminal,

capturing a second image of the eye area at a second position of themobile terminal by means of the camera, and

determining the at least one centration parameter on the basis of thefirst image and the second image,

characterized by

repeated measurement of an acceleration of the mobile terminal during amovement of the mobile terminal from the first position to the secondposition,

determining the at least one centration parameter additionally beingeffected on the basis of the repeated measurement of the acceleration.

Clause 2. The method according to clause 1, characterized in thatdetermining the at least one centration parameter is additionallyeffected on the basis of image angle properties of the camera.

Clause 3. The method according to clause 2, characterized in that themethod additionally comprises determining the image angle properties ofthe camera.

Clause 4. The method according to any of clauses 1 to 3, characterizedby instructions for moving the mobile terminal from the first positionto the second position being issued to a person by the mobile terminal.

Clause 5. The method according to any of clauses 1 to 4, characterizedby:

measuring an orientation of the mobile terminal,determining the centration parameter additionally being based on theorientation of the mobile terminal.

Clause 6. The method according to any of clauses 1 to 4, characterizedby:

measuring an orientation of the mobile terminal, andoutputting an indication if the orientation differs from a predefinedorientation.

Clause 7. The method according to any of clauses 1 to 6, characterizedin that the movement comprises a rectilinear movement toward the eyearea or away from the eye area.

Clause 8. The method according to any of clauses 1 to 7, characterizedin that the movement comprises a movement in a plane in front of the eyearea.

Clause 9. The method according to any of clauses 1 to 8, characterizedin that the movement comprises a three-dimensional movement in front ofthe eye area.

Clause 10. The method according to any of clauses 1 to 9, characterizedin that the at least one centration parameter comprises at least oneparameter from the group comprising a pupillary distance, a measure of aboxing system, a corneal vertex distance and an “as-worn” pantoscopicangle.

Clause 11. The method according to any of clauses 1 to 10, characterizedin that the method comprises capturing a multiplicity of images duringthe movement comprising the first image and the second image,determining the centration parameter being effected on the basis of themultiplicity of images.

Clause 12. The method as claimed in any of claims 1 to 11, characterizedin that the method comprises creating a 3D model on the basis of thefirst image and the second image.

Clause 13. The method according to any of clauses 1 to 12, characterizedin that the method does not use a scale to be fitted on the person.

Clause 14. The method according to any of clauses 1 to 13, characterizedin that at least one capturing from the group comprising capturing thefirst image and capturing the second image comprises capturing a scale,determining the at least one centration parameter additionally beingeffected on the basis of the scale.

Clause 15. The method according to any of clauses 1 to 14, characterizedin that the method furthermore comprises receiving a dimension of aspectacle frame worn by the person, a ratio of the dimension to acorresponding dimension in at least one image from the group comprisingthe first image and the second image serving as size scale.

Clause 16. A method for fitting a spectacle lens by grinding,comprising:

determining at least one centration parameter by means of the methodaccording to any of clauses 1 to 15, andfitting the spectacle lens by grinding on the basis of the at least onecentration parameter.

Clause 17. A computer program for a mobile terminal comprising a programcode which, when it is executed on a processor of the mobile terminal,has the effect that the mobile terminal carries out the method accordingto any of clauses 1 to 15.

Clause 18. A mobile terminal for determining at least one centrationparameter, comprising:

a processor, a camera and an acceleration sensor, the processor beingconfigured for:capturing a first image of an eye area of a person at a first positionof the mobile terminal by means of a camera of the mobile terminal,capturing a second image of the eye area at a second position of themobile terminal by means of the camera, anddetermining the at least one centration parameter on the basis of thefirst image and the second image,characterized in that the processor is furthermore configured for:repeated measurement of an acceleration of the mobile terminal during amovement of the mobile terminal from the first position to the secondposition,determining the at least one centration parameter additionally beingeffected on the basis of the repeated measurement of the acceleration.

Clause 19. The mobile terminal according to clause 18, characterized inthat determining the at least one centration parameter is additionallyeffected on the basis of image angle properties of the camera.

Clause 20. The mobile terminal according to clause 19, characterized inthat the processor is furthermore configured for determining the imageangle properties of the camera.

Clause 21. The mobile terminal according to any of clauses 18 to 20,characterized in that the processor is furthermore configured forissuing instructions for moving the mobile terminal from the firstposition to the second position to a person by means of the mobileterminal.

Clause 22. The mobile terminal according to any of clauses 18 to 21,characterized in that the processor is furthermore configured formeasuring an orientation of the mobile terminal,

determining the centration parameter additionally being based on theorientation of the mobile terminal.

Clause 23. The mobile terminal according to any of clauses 18 to 22,characterized in that the processor is furthermore configured formeasuring an orientation of the mobile terminal, and

outputting an indication if the orientation differs from a predefinedorientation.

Clause 24. The mobile terminal according to any of clauses 18 to 23,characterized in that the at least one centration parameter comprises apupillary distance, a measure of a boxing system, a corneal vertexdistance and/or an “as-worn” pantoscopic angle.

Clause 25. The mobile terminal according to any of clauses 18 to 24,characterized in that the processor is furthermore configured forcapturing a multiplicity of images during the movement comprising thefirst image and the second image, determining the centration parameterbeing effected on the basis of the multiplicity of images.

Clause 26. The mobile terminal according to any of clauses 18 to 25,characterized in that the processor is furthermore configured forcreating a 3D model on the basis of the first image and the secondimage.

Clause 27. A computer-readable nonvolatile data carrier comprisinginstructions which, when they are executed on a mobile terminalcomprising a camera and an acceleration sensor, have the effect that themobile terminal carries out the following steps:

capturing a first image of an eye area of a person at a first positionof the mobile terminal by means of a camera of the mobile terminal,capturing a second image of the eye area at a second position of themobile terminal by means of the camera, anddetermining the at least one centration parameter on the basis of thefirst image and the second image,characterized byrepeated measurement of an acceleration of the mobile terminal during amovement of the mobile terminal from the first position to the secondposition,determining the at least one centration parameter additionally beingeffected on the basis of the repeated measurement of the acceleration.

Clause 28. A data carrier signal which transmits a computer programwhich, when it is executed on a mobile terminal comprising a camera andan acceleration sensor, has the effect that the mobile terminal carriesout the following steps:

capturing a first image of an eye area of a person at a first positionof the mobile terminal by means of a camera of the mobile terminal,capturing a second image of the eye area at a second position of themobile terminal by means of the camera, anddetermining the at least one centration parameter on the basis of thefirst image and the second image,characterized byrepeated measurement of an acceleration of the mobile terminal during amovement of the mobile terminal from the first position to the secondposition,determining the at least one centration parameter additionally beingeffected on the basis of the repeated measurement of the acceleration.

Clause 29. A mobile terminal comprising a processor, a camera, anacceleration sensor and a memory with a computer program stored therein,the processor being configured to control the mobile terminal, on thebasis of the computer program, for carrying out the following steps:

capturing a first image of an eye area of a person at a first positionof the mobile terminal by means of a camera of the mobile terminal,capturing a second image of the eye area at a second position of themobile terminal by means of the camera, anddetermining the at least one centration parameter on the basis of thefirst image and the second image,characterized byrepeated measurement of an acceleration of the mobile terminal during amovement of the mobile terminal from the first position to the secondposition,determining the at least one centration parameter additionally beingeffected on the basis of the repeated measurement of the acceleration.

The foregoing description of the exemplary embodiments of the disclosureillustrates and describes the present invention. Additionally, thedisclosure shows and describes only the exemplary embodiments but, asmentioned above, it is to be understood that the disclosure is capableof use in various other combinations, modifications, and environmentsand is capable of changes or modifications within the scope of theconcept as expressed herein, commensurate with the above teachingsand/or the skill or knowledge of the relevant art.

The term “comprising” (and its grammatical variations) as used herein isused in the inclusive sense of “having” or “including” and not in theexclusive sense of “consisting only of” The terms “a” and “the” as usedherein are understood to encompass the plural as well as the singular.

All publications, patents and patent applications cited in thisspecification are herein incorporated by reference, and for any and allpurposes, as if each individual publication, patent or patentapplication were specifically and individually indicated to beincorporated by reference. In the case of inconsistencies, the presentdisclosure will prevail.

1. A computer-implemented method for determining at least one centrationparameter with a mobile terminal, the at least one centration parameterenabling spectacle lenses to be arranged correctly in a spectacle frame,the method comprising: capturing a first image of an eye area of aperson at a first position of the mobile terminal with a camera of themobile terminal, the mobile terminal having an intrinsic calibration forat least substantially eliminating distortions of the cameracomputationally; capturing a second image of the eye area at a secondposition of the mobile terminal with the camera; and determining the atleast one centration parameter on a basis of the first image and thesecond image, and on a basis of image angle properties of the camera,the image angle properties specifying pixels of an image sensor of thecamera on which an object which is at a specific angle with respect tothe optical axis of the camera is imaged; repeated measurement of anacceleration of the mobile terminal during a movement of the mobileterminal from the first position to the second position being effected;determining the at least one centration parameter additionally beingeffected on the basis of the repeated measurement of the acceleration,wherein the method additionally comprises determining the image angleproperties of the camera, and wherein, for a purpose of determining theimage angle properties, same objects which are at a distance of morethan one meter from the image sensor are captured with in each case twodifferent angular positions of the mobile terminal for a rotation abouta first axis parallel to the surface of the image sensor and about asecond axis perpendicular to the first axis and parallel to the surfaceof the image sensor in a first determination image and a seconddetermination image, and the image angle properties are determined fromimage position displacements of the objects between the respective firstand second determination images for the first axis and the second axisand a respective rotation of the mobile terminal between the twodifferent angular positions.
 2. The method as claimed in claim 1,wherein the method comprises: creating a 3D model of the eye area on thebasis of the first image and the second image; and determining the atleast one centration parameter additionally being effected on the basisof the 3D model of the eye area.
 3. The method as claimed in claim 1,wherein the movement comprises a rectilinear movement toward the eyearea or away from the eye area.
 4. The method as claimed in claim 1,wherein the movement comprises a movement selected from the groupincluding a movement in a plane in front of the eye area and athree-dimensional movement in front of the eye area.
 5. The method asclaimed in claim 1, wherein the at least one centration parametercomprises at least one parameter from the group including a pupillarydistance, a measure of a boxing system of a spectacle frame worn by theperson, a corneal vertex distance, the person wearing a spectacle framewhen the first image and the second image are captured, and an “as-worn”pantoscopic angle of a spectacle frame worn by the person.
 6. Acomputer-implemented method for determining at least one centrationparameter with a mobile terminal, the at least one centration parameterenabling spectacle lenses to be arranged correctly in a spectacle frame,the method comprising: capturing a first image of an eye area of aperson at a first position of the mobile terminal with a camera of themobile terminal; capturing a second image of the eye area at a secondposition of the mobile terminal with the camera; and determining the atleast one centration parameter on a basis of the first image and thesecond image; repeated measurement of an acceleration of the mobileterminal during a movement of the mobile terminal from the firstposition to the second position being effected; determining the at leastone centration parameter additionally being effected on the basis of therepeated measurement of the acceleration, the movement including arectilinear movement parallel to the optical axis of the camera towardthe eye area or away from the eye area, the at least one centrationparameter including a corneal vertex distance, the person wearing aspectacle frame when the first image and the second image are captured,and in each case at least the pupils of the person and the spectacleframe being imaged in the first image and in the second image, wherein adistance between the first position and the second position isascertained on the basis of the repeated measurement of theacceleration; wherein a first distance between the camera and thespectacle frame and a second distance between the camera and a pupil ofthe person are determined on the basis of the ascertained distance andon the basis of image angle properties of the camera, the image angleproperties specifying the pixels of an image sensor of the camera onwhich an object which is at a specific angle with respect to the opticalaxis of the camera is imaged, and wherein the corneal vertex distance isdetermined as a difference between the second distance and the firstdistance.
 7. The method as claimed in claim 6, wherein the methodadditionally comprises determining the image angle properties of thecamera.
 8. The method as claimed in claim 6, wherein the at least onecentration parameter additionally comprises at least one parameter fromthe group including a pupillary distance, a measure of a boxing systemof a spectacle frame worn by the person, and an “as-worn” pantoscopicangle of a spectacle frame worn by the person.
 9. The method as claimedin claim 1, wherein at least one capturing from the group includingcapturing the first image and capturing the second image comprisescapturing a scale, and determining the at least one centration parameteradditionally being effected on the basis of the scale.
 10. The method asclaimed in claim 1, wherein the method furthermore comprises receiving adimension of a spectacle frame worn by the person, a ratio of thedimension to a corresponding dimension in at least one image from thegroup including the first image and the second image serving as sizescale.
 11. The method as claimed in claim 1, wherein: measuring anorientation of the mobile terminal, and determining the centrationparameter additionally being based on the orientation of the mobileterminal.
 12. The method as claimed in claim 1, further comprising:measuring an orientation of the mobile terminal, and outputting anindication if the orientation differs from a predefined orientation. 13.The method as claimed in claim 1, wherein the method comprises capturinga multiplicity of images during the movement, the multiplicity of imagesincluding the first image and the second image, and determining thecentration parameter being effected on the basis of the multiplicity ofimages.
 14. A method for fitting a spectacle lens by grinding,comprising: determining at least one centration parameter by means ofthe method as claimed in claim 1; and fitting the spectacle lens bygrinding on the basis of the at least one centration parameter.
 15. Acomputer program stored on a non-transitory storage medium for a mobileterminal, which has a processor, a camera, and an acceleration sensor,the computer program comprising a program code which, when it isexecuted on a processor of the mobile terminal, has the effect that themobile terminal carries out the method as claimed in claim
 1. 16. Amobile terminal for determining at least one centration parameter, themobile terminal comprising: a processor; a camera; and an accelerationsensor, the mobile terminal having an intrinsic calibration for at leastsubstantially eliminating distortions of the camera computationally, andthe processor being configured for: capturing a first image of an eyearea of a person at a first position of the mobile terminal with acamera of the mobile terminal; capturing a second image of the eye areaat a second position of the mobile terminal with the camera; anddetermining the at least one centration parameter on a basis of thefirst image and the second image, and on a basis of image angleproperties of the camera, the image angle properties specifying thepixels of an image sensor of the camera on which an object which is at aspecific angle with respect to the optical axis of the camera is imaged,the processor furthermore being configured for: repeated measurement ofan acceleration of the mobile terminal during a movement of the mobileterminal from the first position to the second position; and determiningthe at least one centration parameter additionally being effected on thebasis of the repeated measurement of the acceleration, wherein theprocessor is additionally configured for determining the image angleproperties of the camera such that, for a purpose of determining theimage angle properties, same objects which are at a distance of morethan one meter from the image sensor are captured with in each case twodifferent angular positions of the mobile terminal for a rotation abouta first axis parallel to the surface of the image sensor and about asecond axis perpendicular to the first axis and parallel to the surfaceof the image sensor in a first determination image and a seconddetermination image, and the image angle properties are determined fromimage position displacements of the objects between the respective firstand second determination images for the first axis and the second axisand a respective rotation of the mobile terminal between the twodifferent angular positions.
 17. A mobile terminal for determining atleast one centration parameter, comprising: a processor; a camera; andan acceleration sensor, the processor being configured for: capturing afirst image of an eye area of a person at a first position of the mobileterminal with a camera of the mobile terminal; capturing a second imageof the eye area at a second position of the mobile terminal with thecamera; and determining the at least one centration parameter on thebasis of the first image and the second image, the processor furthermorebeing configured for: repeated measurement of an acceleration of themobile terminal during a movement of the mobile terminal from the firstposition to the second position; determining the at least one centrationparameter additionally being effected on the basis of the repeatedmeasurement of the acceleration, the movement including a rectilinearmovement parallel to an optical axis of the camera toward the eye areaor away from the eye area, the at least one centration parameterincluding a corneal vertex distance, the person wearing a spectacleframe when the first image and the second image are captured, and ineach case at least the pupils of the person and the spectacle framebeing imaged in the first image and in the second image, wherein theprocessor is configured to ascertain a distance between the firstposition and the second position on the basis of the repeatedmeasurement of the acceleration, to determine a first distance betweenthe camera and the spectacle frame and a second distance between thecamera and a pupil of the person on the basis of the ascertaineddistance and on the basis of image angle properties of the camera, theimage angle properties specifying the pixels of an image sensor of thecamera on which an object which is at a specific angle with respect tothe optical axis of the camera is imaged, and to determine the cornealvertex distance as a difference between the second distance and thefirst distance.